1. Field
The invention relates to a process for producing biocompatible structures and to a biocompatible microchip.
2. Background Information
Bioelectronics is a rapidly developing research area that combines chemistry, biochemistry and physics. Its aim is to enable communication between electronic apparatuses and living cells. A primary feature of a bioelectronic component is an immobilization of a biomaterial on a conductive or semiconductive substrate and a conversion of biological functions associated with the biological material into electronic signals. Examples of microelectronic components by means of which biological functions can be influenced and controlled include cardiac pacemakers and inner ear auditory prostheses. The development of such bioelectronic components leads to increasingly complex systems, in which a large number of transmission channels for information transmission between an electronic component and the cells to be influenced are required. Thus, for example, retina implants or prostheses for walking/standing are being developed. For this purpose, it is necessary to develop implants which, with numerous contact points, can both stimulate nerve tissue in time sequence and detect a large number of nerve signals that will result spatially and with respect to time. However, metallic electrodes as used in cardiac pacemakers are unsuitable here, since these are recognized as foreign bodies and thus lead to rejection reactions.
Attempts have therefore been made to produce the electrical contact between electronic component and biological tissue with the aid of polymers, such as, for example, silicones or polyurethane. For this purpose, the polymers must however be electrically conductive and additionally biocompatible, i.e. the materials must not give rise to any rejection reaction. In order to be able to contact nerve paths in a specific manner, a structuring of these materials or of the substrates used, for example mini-silicon wafers having dimensions in the region of a few millimeters, is necessary. The size of the structures, such as pyramids or holes, produced in or on the substrate is in a range from 10 μm to about 70 μm.
The most critical element in bioelectronics is the interface between electronics and biological tissue. In order to produce suitable contact, the procedure adopted to date, for example, is first to etch about 25 μm deep pyramidal indentations into a silicon chip. The indentations are then first partly filled with conductive silicone and a second layer of nonconductive silicone is then applied. The polymers are then cross-linked and the structured flexible layer is then removed from the silicon chip. Finally, contact with the silicon protuberances formed on the surface of the flexible layer is produced by individual connecting lines. A similar principle can be used to produce rectangular trenches having tiny dimensions from polyurethane, which trenches can act as microcells for the cultivation of nerve cells.
In order to be able to connect individual neurons specifically to microsystems, supporting structures, such as, for example, trench-like microstructures, are provided on the surface of the substrate. Furthermore, adhesion promoters which facilitate the growth of cells on the surface of the substrate are applied to the surface. In such structures, sown cells grow into network-like structures, and biohybrid systems in the form of microchips covered with cell growth form. Materials which promote cell growth and support the adhesion of the cells are suitable as adhesion promoters at the interface.
In spite of the numerous activities in the area of bioelectronics, this area is still in an experimental stage, so that considerable progress is necessary, particularly in the region of the interface between electronic component and cells, in order to make this area accessible to medical use in practice.